Treatment of tannin extracts



Patented Got. 20, 1936 TREATMENT OF TANNIN EXTRACTS Fernando Fontana, Buenos Aires, Argentina, assignor to La Forestal Argentina, S. A. de Tierras, Maderas y Explotaciones Comerciales e Industriales, Buenos Aires, Argentina, a company of Argentina No Drawing. Application May 10, 1935, Serial No.

20,891. In Argentina April 9, 1935 g 3 Claims.

The present invention relates to the treatment of tannin extracts, more especially quebracho extracts, and in particular to a new and improved process whereby it is possible to obtain, on the one hand, an extract clarified by means of a novel method and, on the other hand, residues with which solutions specially adapted for the tanning of certain kinds of leather may be prepared.

The principal object of the invention is the provision of a novel method of clarifying tannin extracts whereby the use or addition of foreign matter is obviated, so that apart from the clarified extract, unadulterated residues are obtained.

A further object of the invention is to provide solutions specially adapted for the tanning of certain classes of leather by making use of the unadulterated residues of the aforesaid method of clarification.

It has been customary for many years to clarify tanning extracts by treating the extract with a coagulating substance such as blood, glue and alumina, and thereupon separating the coagulum by filtration, decantation or the like methods.

There are many disadvantages associated with the use of such coagulants, the most important being the difiiculty of obtaining them easily and cheaply in a tannin factory. Moreover the precipitate or coagulum obtained is of very little value owing to the presence of the clarifying agent used which, furthermore, does not always separate out completely from the clarified tannin.

The process according to the present invention consists essentially in the clarification of the extract without the use or addition of foreign matter in the form of coagulants or the like, so that both the clarified extract and the residues are obtained in an unadulterated condition.

Thus, apart from the production of. unadulterated clarified extracts, the present invention has the following advantages:

Among the varioustypes of leather produced by the leather industry there are two very prominent classes, namely, sole leather and upper leather for shoes, each of which ought to possess its distinctive properties, determined not only by the use to which the leather is to be put but also by the basis on which it is sold. Sole leather should preferably be very stout and relatively hard and is sold by weight, whereas upper leather should be much more flexible and is sold by area. The current practice of the present day is to use the same tanning solution for tanning both these classes of leather, a certain degree of differentiation being achieved by modifying the conditions of treatment. The result of this is, as will be readily understood by those skilled in the art, that the sole leather obtained is lighter than it could be whereas the upper leather is harder and heavier than is necessary.

This difliculty, objectionable alike from the tion and for the upper leather, a solution deficient in such heavier material.

The process of the present invention allows such special solutions to be obtained in. an easy and simple manner, principally due to the fact that by the novel clarification method the greater partof the heavier material is removed from theextract thus giving a clarified solution which in it? self complies with the requirements for the tanning of upper leather.

Moreover, the residues that is to say, the heavier materials separated may, since they are quite un adulterated, be added in any desired quantities to tanning solutions intended for tanning sole l'eather, so as to form a solution which will give a much heavier and stouter leatherfIn this way, not only is it possible to obtain improved extracts, but these may readily be used'in themost economical and appropriate manner for the production of high grade leathers.

The materials which in accordance with the present process act as coagulants'are those which are already present in colloidal phase in the industrial tannin solutions and especially in quebracho extract. To enable said materials to act as clarifiers, it is necessary to break down the colloidal phase, and I have found that this can be simply achieved by rapidly coolingthe cloudy ex& tract. This gives'rise to the formation of a flocculent mass, which, as it were'enmeshes all the material in suspension and precipitates rapidly, leaving a perfectly clear solution.

Thus, for example, in the case of a solution of quebracho extract giving the following initial analysis:

I cause this solution to pass through a coiled pipe immersed in a bath of water at C. in such a manner that the temperature of the solution is brought down to 15 C. in two minutes. It will then be noted that in the tank or vessel in which the treated solution is collected, a precipitate forms by flocculization, which is Well defined and separates out from the perfectly clarified tannin solution, the analysis of which shows a complete absence of insoluble material and of opacity. No filtering or centrifuging is necessary.

The foregoing example is merely illustrative, as in practice the degree and time of cooling will have to be varied in accordance with the concentration of the original solution and the class of tanning extract therein contained.

My novel process differs essentially from the known decantation process whereby the insoluble materials are separated out at different temperatures, since the latter method does not clarify the solution or remove therefrom the matter which is in colloidal suspension, nor is it to be considered as a continuous process, whereas the feature of continuity is one of the outstanding advantages of my novel method.

The utilization of the residues for preparing special solutions is based on the following considerations.

Those materials present in quebracho extract, which in international analyses are termed insolubles are for the mostpart tannin substances of higher molecular weight than the quebracho tannins which are soluble in cold water. Thus either by the addition of these insoluble portions to the natural tannin extracts or by the partial elimination therefrom of the soluble tannins, a tanning solution richer in tannins of high molecularweight will be obtained, which will allow the tanner to produce leathers having a greater value than those'now obtained.

The difference in the results obtained by using different classes of tanning solutions has already been observed in the leather industry. These differences are attributed chiefly, apart from the system of tanning employed, to the fact that certain tannins contain fermentable substances which afiect the fixation of the tannins and at the same time subject the hide to be tanned to conditions favourable to such purpose. One point, however, which has hitherto. not been thoroughly investigated is the importance of the tannins or substances which are absorbed by the hide and which enter into chemical combination with the hide material.

Their importance lies in the fact that the weight of leather obtained from a given quantity of hide substance varies with the molecular weight of the tannin employed. It follows logically therefore, that if it is desired to produce heavy leathers, as for shoe'soles, it is necessary to prepare tannins of high molecular weight for use in the tanning thereof. v Natural quebracho extract is one of the extracts richest in tannins of high molecular weight.

It will be seen therefore, that by applying my novel process to tanning extracts and more especially to quebracho extract, I obtain not only a clear and unadulterated solution particularly suitable for the manufacture of upper leathers, but at the same time I obtain unadulterated residues which, containing the high molecular weight tannins, may readily be added to other solutions so as to increase their concentration of these tannins and render them especially suitable for the production of heavy sole leathers.

Both of these features are deemed to be comprised within the scope of the present invention as defined in the appended claims.

What I claim is:

l. A process for clarifying tanning extracts, including quebracho extract, containing suspended and colloidal matter, said process consisting in subjecting the tanning extract alone to rapid cooling so as to cause coagulation and precipitation of the said suspended and colloidal matter to form a coagulum and a clear supernatant liquor, and separating said coagulum from said liquor.

2. A method of preparing a tanning solution especially adapted for the tanning of relatively flexible and light upper leather, comprising treating a tanning extract containing suspended and colloidal matter, said matter including tannins of relatively high molecular weight, and substances in solution including tannins of relatively low molecular weight, by subjecting said tanning extract to rapid cooling so as to cause precipitation of the matter in suspension to form a coagulum rich in tannins of relatively high molecular weight and a clear supernatant tanning solution deficient in said tannins, and separating said coagulum from said supernatant tanning solution.

3. A method of preparing a tanning solution especially adapted for the tanning of relatively heavy and stout sole leather, comprising treating a tanning extract containing suspended and colloidal matter, said matter including tannins of relatively high molecular weight, and substances in solution including tannins of relatively low molecuar weight, by subjecting said tanning extract to rapid cooling so as to causeprecipitation of the matter in suspension to form a coagulum rich in tannins of relatively high molecular weight and a clear supernatant liquor deficient in said tannins, separating said coagulum from said supernatant liquor and adding said coagulum to a normal tanning solution to increase its concentration of tannins of relatively high molecular weight.

FERNANDO FONTANA. 

